Blame!: Fort of Silicon Creatures

Steel and rust. The City structure has endlessly propagated itself for so many years that the reason for such growth has long since been forgotten. Even within such a techo-dystopia, humans still exist: The Electrofishers. Driven to the brink of extinction, they are visited by a traveller—a man named Killy. But will his presence bring the Electrofishers ruination or hope … ? (Source: Kodansha USA)

In a future version of Earth, there is a city grown so chaotically massive that its inhabitants no longer recall what “land” is. Within this megastructure the silent, stoic Killy is on a mission to find the Net Terminal Gene—a genetic mutation that once allowed humans to access the cybernetic NetSphere. Armed with a powerful Graviton Beam Emitter, Killy fends off waves of attacks from fellow humans, cyborgs and silicon-based lifeforms. Along the way, he encounters a highly-skilled scientist whose body has deteriorated from a lengthy imprisonment who promises to help Killy find the Net Terminal Gene, once she settles a score for herself… (Source: Kodansha USA) *Note: Includes one extra chapter.*